1. Field of the Invention
The present invention relates to methods for producing complete human antibodies and, more particularly, to a method for producing human antibodies of agonist, antagonist and/or inverse agonist to a biological receptor and the antibodies produced by the same method.
2. Description of Related Art
Generally speaking, drugs must reach specific sites in the body to achieve pharmaceutical effects. Most of these sites are composed of cells that provide target molecules, i.e., receptors, to bind with, or interact with the molecules of drugs. The drug-receptor interaction or binding may lead to either an activation of the receptor, which ultimately results in a biological response; or a blockade of the receptor, which hinder the receptor activation by other drugs or ligands. Pharmacodynamics thus defines an agonist as a drug has the same or similar effect as a group of drugs or ligands. Accordingly, when a drug counteracts the effect of another drug or group of ligands, it is called an antagonist. In the situation where a ligand produces an effect opposite to that of the agonist by occupying the same receptor, it is called an inverse agonist.
Human antibodies have been successfully used for therapeutic drugs against various diseases. These diseases are traditionally infectious diseases, such as infections by respiratory syncytial virus (RSV). Recently, however, antibodies are increasingly used in the therapy of many other disorders, including autoimmune disorders and malignancies like metastastic breast cancer, non-Hodgkin's lymphoma, chronic lymphocytic leukemia and acute myeloid leukemia. Prophylactic use against organ rejection or blood clotting during angioplasty has also been achieved. In general, therapeutically monoclonal antibodies (MAbs) clinically available so far act by binding to ligands, e.g., virus or cytokines, thereby preventing their interactions with the respective receptors and thus blocking unwanted natural effector functions. Other existing receptor-specific monoclonal antibodies have been confined mostly to direct defensive and demolishing mechanisms to receptor-bearing targets such as malignant cells, thereby mediate their death. Although these systems have been extremely effective, they are not readily adapted to resolve more physiologic situation in which receptor-acting antibodies have pharmacodynamical activities.
While yet to be fully available, antibodies with a defined pharmacologic activity have been reported lately. For example, WO 00/32231, U.S. Pat. No. 5,811,097, U.S. Pat. No. 5,855,887 and U.S. Pat. No. 6,051,227 disclose MAbs to mouse CD152 (cytotoxic T lymphocyte antigen-4, CTLA-4) derived from hamsters immunized with a mouse CD152-human IgG1 fusion protein. As CD152 belongs to a groups of immunomodulating receptors that collectively termed as CD28 superfamily and represents a receptor negatively involved in T-lymphocyte co-stimulatory pathways regulating both humoral (antibody-mediated) and cellular immune response, an anti-tumor immune response that shows specificity and memory against the growing tumor was thereafter provoked by injecting antibodies specific for the receptor into mice with tumors (Leach et al., Science 271:1734, 1996). The idea behind this “CTLA-4 (antibody) blockade” approach is that the negative function of CD152 can be blocked with antibodies, therefore acting as antagonists, which may allow the activation or sustenance of residual but effective anti-tumor immunity.
Blocking the negative regulatory role for CD152 inhibition of the immune response provides a novel therapeutic technology, allowing the immune system to recognize and more vigorously attack foreign pathogens and cancers. However, antibodies with murine sequences often elicit immunological responses in the patient (human anti-mouse response) when administered to a human patient. Therefore, it is desirable to prepare fully human antibodies that are void of non-human sequences. By immunizing engineered transgenic mice harboring human immunoglobulin genes, fully human antibodies against CD152 have been reported (see, e.g., WO 00/37504, WO 01/14424, U.S. Pat. Nos. 6,150,584 and 6,682,736). The most exciting conclusion from continuous studies of these anti-CD152 blocking antibodies is the potential for antagonistic antibodies to strengthen the immune response against certain tumors and pathogens, leading to the reduction or elimination of well-established tumors as well as enhancement of antibody reaction to vaccinations.
Being an inhibitory receptor of the CD28 receptor family that plays a key role in regulating T cell activation, agonist binding to CD152 reduces T cell proliferation and cytokine production, resulting in attenuated immune responses. Endogenous agonists include CD80 and CD86 present on antigen-presenting cells (APCs) and CD152 ligation mediates tolerance and anergy. As shown by many and generally accepted, blockade of CD152-agonist interactions, provided by antagonistic antibodies, reduces the inhibition mediated through the CD152 signaling. However, comprehensive receptor-binding drugs should offer activities stopping the binding of the native agent without eliciting a response, i.e., antagonists; but also triggering the same or even opposite events as the native ligand, i.e., agonists or inverse agonists, respectively. In the case of CD152, the use of an agonist would therefore promote organ transplantation and blockade of autoimmune disease by the inhibitory costimulatory pathway. Clearly, it would offer solution to clinical conditions such as allergies, graft versus host disease and graft rejection. On the other hand, both designed and serendipitous inverse agonists could result in medications that display greater efficacy in cancer therapy.
Currently available anti-human CD152 huMAbs only act as antagonistic blocking agents have limited their usefulness in clinical applications. The present invention addresses needs for molecules having varied abilities to preferentially bind to and/or signal through CD152 receptor and methods of screening such molecules for selected and differential manipulation of T cell responses in vitro. Such human antibody molecules would be of beneficial use in a variety of applications, including, e.g., therapeutic and prophylactic treatments and vaccinations. The present invention fulfills these and other needs.
More details about the related prior art in this field can be found in the references listed below:    1. Chin L T, Hinkula J, Levi M, Ohlin M, Wahren B, Borrebaeck C A K. (1994) Site-directed primary in vitro immunization: Production of HIV-1 neutralizing human monoclonal antibodies from sero-negative donors. Immunology 81: 428-34.    2. Chin L T, Malmborg A C, Kristensson K, Hinkula J, Borrebaeck, C A K. (1995) Mimicking the humoral immune response in vitro results in antigen-specific isotype switching by autologous T helper cells. Eur. J. Immunol. 25:657-663.    3. Leach D R, Krummel M F, Allison J P. (1996) Enhancement of antitumor immunity by CTLA-4 blockade. Science. 271:1734-6.    4. Linsley P S, Brady W, Urnes M, Grosmaire L S, Damle N K, Ledbetter J A. (1991) CTLA-4 is a second receptor for the B cell activation antigen B7. J. Exp. Med. 174:561-9.    5. Demotz S, Lanzavecchia A, Eisel U, Niemann H, Widmann C, Corradin G. (1989) Delineation of several DR-restricted tetanus toxin T cell epitopes. T Immunol. 142:394-402.